Thermionic tube



Patented Dec. 1 1936 UNITED STATES I THERMIONIG TUBE Earl L. Koch,Chicago, Ill.,

assignor, by mesne assignments, to Radio Patents Corporation, New York,N. Y., a corporation of'New York Original application Mar ch 21, 1931,Serial No.

524,254. Divided and this application July 3,:

1934, Serial No. 733,547

3 Claims. (01. 250-415) This invention relates to improvements inthermionic tubes such as are employed in radio telegraphy and telephony.

This application is a division of application Serial Number 524,254,filed March 21, 1931.

Thermionic tubes of the three element type which usually include ananode or plate, a cath ode and a grid, are open to serious objectionparticularly with respect to capacity efiects between the grid and theplate. These effects are more pronounced when high frequencyoscillations are employed.

An object of the invention is the provision of a thermionic tube inwhich this objection is obviated without the introduction of additionalelements or circuits.

A further object of the invention is the provision in a transmitting, orpower, electronic tube an anode or plate which further functions as apart of the. cooling system of the tube and which is statically shieldedfrom the grid by the cathode.

Other objects will be apparent to those skilled in the art upon aperusal of this specification.

Referring to the drawing:

Figure 1 is a sectional elevation of the new and improved electronictube,

Figure 2 is a transverse sectional view taken along the line 22 ofFigure 1,

Figure 3 is a diagrammatic sketch showing the voltage gradient between acathode and a plate when the cathode is heated to various degrees, and

Figure 4 is a diagrammatic sketch similar to Figure 3.

Referring to Figure 3 which shows graphically the voltage relationbetween the cathode and the anode or plate of a thermionic tube atvarious cathode temperatures, the oblique straight line 23 correspondsto an unheated cathode which is not emitting electrons. The curves 24,25, and 26 represent increasing cathode temperatures, the cathodeprogressively emitting electrons at a greater rate as the heatingincreases. The progressively increasing deviation of these curves fromthe straight line 23 graphically illustrates the effect usually termedthe space. charge effect. The presence of innumerable electrons betweenthe cathode and the plate results in this eifect,

, the concentration of such electrons being greatest at the cathode oradjacent thereto. It will be seen from the curve 25 that there is novoltage gradient adjacent the cathode at the cathode temperaturecorresponding to this curve, which is substantially horizontal, adjacentthe cathode. The curve 26 corresponds to operating conditions of thetube and it will be noticed that the concentration of electrons adjacentthe cathodefis sufficient to produce av zone about and in spaced'relationto the cathode diagrammatically indicated by the dottedline.21. In this zone there is an actual negative voltage. In thisspecification the zone within the surface 21 will be termed the virtualcathode region.

According to the present invention, the grid is located about andsurrounding the cathode structure and the cathode is preferably formedof zigzagfilaments 20, Figure 1, the grid 22 is preferably in the formof a cylinder surrounding and concentric with the cathode structure.When the tubeis operating, the filament structure separates grid fromthe plate by a'cloud of electrons which substantially reduce or nullifythe capacity effect between the grid and the plate. The grid ispreferably located within the virtual cathode region. When the cathodeis cold, a definite capacity exists between the grid and the plate butunder operating conditions the cloud of electrons effectively reduces ornullifies this capacity. In the graphic illustration in Figure 4 thegrid 22 represented by the dotted line is located very close to thecathode 20 so that it is well within the virtual cathode region as shownby the voltage curve.

Referring to the tube, Figure 1, it is provided with a hollowcylindrical member 2| which forms the plate. This member is preferablyconstructed of copper and is provided with nipples 52 which are locatedinternally near each end of the member 2|. By connecting hoses to thenipples 52 cooling water may be passed through the member 2| for coolingthe tube while the same is in operation. The ends 5| of the member 2|are each tapered to a knife edge. which is sealed into inwardly directednecks 53 of the glass body IE3 of the tube.

Inwardly extending collar I4 is positioned adjacent to and surroundingeach end of the plate 2|. These collars may be secured in any wellknownmanner to inwardly extending bosses l3 which form a part of the glassenvelope l0. They extend inwardly beyond the bosses l3 and are providedwith holes or openings whereby a series of hooks [5 may be mounted. Thehooks l5 support rings I6 of glass or other suitable insulating materialand these rings form supports for a circumferential series of hooks l1upon which the cathode 20 may be strung in the form of a zigzagfilament.

The grid or control element 22 which is preferably in the form of ashort cylinder is located around and substantially concentric with thecathode. The envelope ID has a boss l9 formed in one side thereof whichcarries a metallic collar l8 which in turn supports the grid 22. Aconductor 28 connected to the grid 22 extends through the boss l9 andprovides external means for connecting to the grid 22.

Leads 29 of the cathode may extend through the press 30 provided at asuitable position in the glass envelope ID. A conductor 3| which iswelded to one of the nipples 52 of the plate 2| provides a plateconnection. This conductor together with its weld is positioned outsideof the glass envelope II]. It is of course understood that the cathode,the grid and the plate are enclosed in an evacuated vessel H) which iscomprised of both metal and glass.

It will be noted that the grid 22 is of substantially less length thanthat of the cathode. Therefore, the electron cloud not only shields theinterior of the grid 22 but it also shields the ends of the grid fromcapacity eifects with the plate.

Although the invention has been disclosed in connection with thespecific details of preferred embodiments thereof, it must be understoodthat such details are not intended to be limitative of the inventionexcept insofar as set forth in the accompanying claims.

What is claimed is:

1. A thermionic tube comprising, a cathode having a zig-zag filamentformed into an annular cage, a metallic water tube within and parallelto said cage and forming an anode, said metallic tube having straightextensions the ends of which form knife edges, a metallic sleevesurrounding and closely adjacent to said cage and constituting a controlelement and a glass envelope sealed to said knife edges and forming,together with the metallic tube, a sealed enclosure for the cathode andthe control element through which a cooling fluid may pass in a straightline.

2. A thermionic tube comprising a glass envelope having inwardlydirected necks at each end thereof, inwardly extending bosses locatednear said necks, and a boss in the side wall thereof, a metallic tubehaving knife edged ends sealed into said necks and forming with saidglass envelope a gas tight casing, said metallic tube forming an anodeand serving as means for conducting heat to a stream of water passingtherethrough, a cathode comprised of a zig-zag filament formed into anannular cage positioned about and substantially concentric with saidmetallic tube, supports for said cage carried by said inwardly extendingbosses, and a metallic sleeve supported by the boss in said side walland constituting a control element, the space between said controlelement and said cathode being less than that between the cathode andthe anode.

3. A thermionic tube according to claim 1 in which the glass envelope isprovided with inwardly extending bosses at each end which support theannular filament cage in space relation to the water tube forming theanode, and a third inwardly extending boss spaced apart from said firstbosses and supporting said sleeve closely adjacent to the cage formingsaid cathode.

EARL L. KOCH.

